Vessels for separating contaminants from liquids are well known in the art and are generally in the form of a cylindrical tank with a conical bottom, where the apex of the conical bottom is lower than the outer side thereof.
Inlets may be positioned so as to produce a spiral flow of the liquid in the vessel and outlets may be positioned at the bottom, top and sides of the vessel to enable the drawing off of various fractions of the separated liquid stream, depending on its relative specific gravity.
For the purposes of this specification, a vessel or vessels of aforementioned type will be hereinafter referred to as a “treatment vessel” or “treatment vessels”.
The inlet of a treatment vessel is typically situated at the outer edge of the treatment vessel, and is typically arranged in such a manner so as to introduce liquid tangentially and thereby create laminar, spiral flow within the treatment vessel. As the liquid nears the centre of the treatment vessel, the speed decreases and the direction of the flow is changed to a vertical up and down flow towards the top and bottom outlets.
It is preferred that no spiral flow takes place at the centre part of the treatment vessel so as to allow the contaminants to separate.
Separation takes place within the treatment vessel as the speed of flow slows toward the centre of the treatment vessel. Thus, while contaminants are suspended at the rate of flow at the outer part of the treatment vessel, these will be released as the speed of flow decreases toward the centre of the treatment vessel and will separate into their fractions depending on their specific gravity.
Separation can be aided by the prior addition of a variety of chemical substances. The methods for introducing contaminated liquids tangentially into a treatment vessel so as to produce spiral flows and the methods for operating such treatment vessels are well known.
It is often the practice to use more than one treatment vessel within a single separator system where more than one operation is required within the separator system. Thus, one treatment vessel may be used for removing those contaminants where the specific gravity of the contaminants is heavier than the carrying liquid, and another treatment vessel may be used to concentrate the contaminants removed.
A problem with existing treatment vessels used in separator systems is that the heaviest contaminants are directed downward toward the apex of the conical bottom of the treatment vessel and can build up a plug which does not flow out of the treatment vessel as desired.
The inventor of the present invention has previously provided a method of mitigating plugging of the bottom outlet of the treatment vessel by reintroducing clarified liquid obtained from a treatment vessel within the separator system in a manner so as to produce a downward spiral flow to scour out the conical portion of the treatment vessel. However, it has been found that the effectiveness of the method over prolonged periods of time can sometimes be compromised by the formation of “rat-holes” within the settling sediment, since upon its mechanical removal the sediment adheres to the walls of the conical portion. Further, access to the bottom portion of the treatment vessel for maintenance and cleaning, in the eventuality of “rat-hole” formation can sometimes be very difficult.
The present invention seeks to mitigate the possibility of “rat-holing” and subsequent plugging in treatment vessels by the separation of heavy contaminants therein and which increases the efficiency of operation of same beyond that of prior treatment vessels and clarifiers.